Time slot and carrier frequency allocation in a network

ABSTRACT

In an OFDM-TDMA power line communication system, time slot and carrier frequencies are assigned in a manner that reallocates time slots and carrier frequencies to enhance the efficiency of utilization of bandwidth. The reassignments are communicated between transmitting and receiving stations by transmitting tone maps that designate the reassignment of the time slots and carriers. Several variations are presented depending upon the circumstances of channel use and prior assignment of time slots and channels.

CROSS REFERENCE TO RELATED DOCUMENTS

This application is related to U.S. Provisional patent applicationSerial No. 60/463,457 filed Apr. 16, 2003 to Iwamura, entitled “CarrierManagement for a Network” which is hereby incorporated herein byreference.

FIELD OF THE INVENTION

This invention relates generally to the field of multiplexcommunication. More particularly, certain embodiments consistent withthe present invention relate to a time/frequency slot allocationarrangement particularly suitable to power line communication (PLC)systems or other multiplexed multiple carrier communication systems.

BACKGROUND OF THE INVENTION

Power Line Communication (PLC) is becoming a popular network technologyin the consumer electronics market since the existing electrical wiringof a house is used for data traffic without need for separate datawiring. PLC networks also do not have the security issues of wirelessnetworks. Quite a few products including, but not limited to, bridges,routers and other products are currently commercially available fromseveral manufacturers in the consumer market.

At this writing, the current PLC technology employs the technologies ofOFDM (Orthogonal Frequency Division Multiplex) and CSMA/CA (CarrierSense Multiple Access with Collision Avoidance. OFDM is a knownmodulation scheme that uses multiple carriers in a spread spectrumtransmission scheme to transmit information. CSMA/CA is a known channelaccess protocol that is used in Ethernet. In such PLC systems,transmitters and receivers exchange information that identifiesavailable/usable carriers (called a “tone map”) every several seconds.Some carriers cannot be used because of noise interference (e.g., frommotors, switching power regulators and other sources of electricalinterference). The transmitter transmits data using the availablecarriers and leaves the others unused.

The operation of the CSMA/CA channel access mechanism is as follows.Before the transmitter starts a transmission, the transmitter firstdetects the network bus. If the bus is not busy, the transmitter startstransmission. When the bus is busy, the transmitter re-triestransmission after a random waiting time.

OVERVIEW OF CERTAIN EMBODIMENTS OF THE INVENTION

The present invention relates generally to multiplexed communicationsystems and methods. Objects, advantages and features of the inventionwill become apparent to those skilled in the art upon consideration ofthe following detailed description of the invention.

In one embodiment consistent with the present invention, a time slot andcarrier allocation method for time division multiple access (TDMA)multiple carrier communications involves determining from a tone mapthat first and second time slots are generally allocated to a first anda second receiver respectively; determining that a carrier is unusedduring the first time slot; and transmitting a new tone map to the firstand second receivers that specifies that the unused carrier is to bereallocated to the second receiver.

In another embodiment consistent with the present invention, a time slotand carrier allocation method for time division multiple access (TDMA)multiple carrier communications involves determining from a tone mapthat a first time slot is generally allocated to a first receiver forreceipt of a single stream of data for each time slot usage; determiningthat a carrier is unused during the first time slot; determining that asecond stream of data is to be sent to the first receiver; andtransmitting a new tone map to the first receiver that specifies thatthe unused carrier is to be reallocated to the second stream of data.

In still another embodiment consistent with the present invention, atime slot and carrier allocation method for time division multipleaccess (TDMA) multiple carrier communications involves determining froma tone map that first and second time slots are generally allocated to afirst and a second receiver respectively; determining from the tone mapthat the first and second receivers are able to receive using a commonset of carriers; determining that a single data stream is to betransmitted to the first and second receivers; and transmitting a newtone map to the first and second receivers that specifies that the firstand second receivers are to receive the single data stream using thecommon set of carriers during one or more designated time slots.

In still another embodiment, a time slot and carrier allocation methodfor time division multiple access (TDMA) multiple carrier communicationsinvolves determining if a time slot is available, and if so assigning astream of data destined for a specified receiver to the time slot; if notime slot is available, determining if a time slot having the samedestination is available; and if a time slot having the same destinationis available, assigning a carrier in the time slot to the stream ofdata.

In yet another embodiment consistent with the present invention, a timeslot and carrier allocation method for time division multiple access(TDMA) multiple carrier communications involves determining if a numberof commonly used carriers between two or more receivers is greater thana threshold number of carriers; if so, calculating a number of timeslots as a carriers divided by the number of commonly used carriers;assigning the time slots to the receivers; and assigning a stream ofdata to the common carriers.

Other embodiments are also possible within the scope of the presentinvention. The above descriptions are intended to illustrate exemplaryembodiments of the invention which will be best understood inconjunction with the detailed description to follow, and are notintended to limit the scope of the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the invention believed to be novel are set forth withparticularity in the appended claims. The invention itself however, bothas to organization and method of operation, together with objects andadvantages thereof, may be best understood by reference to the followingdetailed description of the invention, which describes certain exemplaryembodiments of the invention, taken in conjunction with the accompanyingdrawings in which:

FIG. 1 is a block diagram of a power line communication networkconsistent with certain embodiments of the present invention.

FIG. 2 is a block diagram of an exemplary Server device consistent withcertain embodiments of the present invention.

FIG. 3 is a block diagram of an exemplary power line interfaceconsistent with certain embodiments of the present invention.

FIG. 4 is a block diagram of an exemplary Client consistent with certainembodiments of the present invention.

FIG. 5 is a first illustrative example tone map table.

FIG. 6 is a second illustrative example tone map table.

FIG. 7 is a third illustrative example tone map table.

FIG. 8 is a fourth illustrative example tone map table.

FIG. 9, which is made up of FIG. 9A and FIG. 9B, is a flow chart of acarrier assignment algorithm consistent with certain embodiments of thepresent invention.

FIG. 10 is a fifth illustrative example tone map table:

FIG. 11 is a sixth illustrative example tone map table.

FIG. 12 is a seventh illustrative example tone map table.

FIG. 13 is a eighth illustrative example tone map table.

FIG. 14 shows an illustrative time slot assignment algorithm forbroadcast communications.

DETAILED DESCRIPTION OF THE INVENTION

While this invention is susceptible of embodiment in many differentforms, there is shown in the drawings and will herein be described indetail specific embodiments, with the understanding that the presentdisclosure is to be considered as an example of the principles of theinvention and not intended to limit the invention to the specificembodiments shown and described. In the description below, likereference numerals are used to describe the same, similar orcorresponding parts in the several views of the drawings.

The above-mentioned CSMA/CA system does not generally provide sufficientQoS (Quality of Service) for audio/video transmission. The nextgeneration network, as currently proposed, will introduce TDMA (TimeDivision Multiplex Access) and time slot management to guarantee ahigher QoS level. In this next generation system, a bus master dividesthe time axis to small time slots and assigns some of them to eachcommunication based on its priority. Each time slot in this proposednext generation network is reserved for a single stream of data destinedfor a single receiver.

Unfortunately, in such a proposed system, carriers may not be usedefficiently. When the transmitter communicates with a receiver, it usesonly the available carriers—that is, carriers that are able tocommunicate with a particular receiver with a particular servicequality. The other unavailable carriers are left unused. When only asmall number of carriers are available, the bandwidth available inunavailable carriers is not negligible. Also, another problem can occurwhen the transmitter broadcasts a stream to multiple receivers. Sincethe availability of carriers is highly dependent upon each network pathbetween transmitter and receiver, the transmitter sends the same datarepeatedly to each receiver using different carriers. This redundanttransmission is wasteful of bandwidth and is compounded when the samemessage is destined for many receivers.

FIG. 1 illustrates an example of a simple home PLC system. Server 104,Client (1) 108 and Client (2) 112 are connected to the home power line116 for use as a physical data distribution medium for the currentexemplary network. Power line 116 serves further serves to distributepower to electrical outlets such as 120 and 124. Server 104 storesvarious types of data possibly including, but not limited to,audio/video data and sends a stream data to a Client. Also, Server 104receives an audio/video stream, e.g., from a cable television network130 and redistributes it to the Clients. For purposes of this document,the word “stream” is used for both isochronous and asynchronouscommunications.

An exemplary server such as Server 104 is depicted in FIG. 2 in blockdiagram form. Tuner Front-end 202 receives an RF signal from the cablenetwork 130. Codec block 206 decodes the demodulated digital signal fromTuner Front-end 202 using Memory 210. The decoded video signal is thenDigital to Analog converted in D/A Converter 214 for display on aDisplay 218 such as a monitor. A decoded audio signal is similarlyDigital to Analog converted in D/A converter 222, amplified in anamplifier 226 and ultimately sent to a loudspeaker or loudspeaker system230. To record a video stream, Codec 206 sends the video stream to HDD234 through Bus 238 and Interface 242. To replay the recorded stream,Codec 206 receives the stream from HDD 234 via interface 242 and bus238, decodes it and the audio and video are converted to analog at 214and 222 and further processed as previously described.

Assume that Server 104 sends a video stream to client 108 over powerline 116 (or other suitable transmission medium). The stream from tunerfront-end 202 is sent to a PLC interface 250 through Codec 206. PLCinterface 250 sends the stream to client 108. Similarly, to play therecorded stream in HDD 234, the stream from HDD 234 is sent to PLCinterface 250 and sent to client 108 over the power line 116. PLCinterface 250 may include an encrypter and a decrypter (not shown). Thispermits all of the communication to be encrypted before sending to thepower line 116 and decrypted after receiving from the power line 116.The server can be controlled by user inputs into a Key Pad 254 or RemoteCommander 258. Key Pad 254 sends commands to a central processing unit(CPU) 264 through Interface 268 and Bus 238. Similarly, Remote Commander258 sends commands to CPU 264 through an infrared or other wirelessInterface 272 and Bus 238. CPU 264 operates under program control inconjunction with its associated memory 274 to oversee operation of theserver. Server 104 may also incorporate a modem 280 for communicationbetween the server 104 and a computer network or the Internet. Modem 280can be, for example, an ADSL modem or a cable modem.

FIG. 3 illustrates an exemplary block diagram of an embodiment of PLCinterface 250. In this exemplary embodiment, data to be transmitted arereceived from Bus 238 by Bus Interface 304 and can be stored in BufferMemory 308 if necessary. Error correction code is added to the data inForward Error Correction (FEC) Encoder 312. Interleaver 316 interleavesthe resulting error correction encoded data. The interleaver 316 spreadsout data to minimize errors in consecutive bits that might otherwise becaused by transient noise, etc., thus enhancing the ability to correcterrors. A Serial-to-Parallel converter (S/P) 320 converts theinterleaved data to parallel data. The parallel signals from S/P 320 aremodulated by a Modulator 324 and sent to Inverse Fast Fourier Transform(IFFT) block 330.

A second path for transmitted data can also be provided through FEC 334,Interleaver 338, S/P 342 and Modulator 346 for a second stream. Thecomponents 334 through 346 of the second path function in the samemanner as that of components 312 through 324. If the performance ofcomponents 312 through 324 is fast enough to process two streams withina required time, components 334 through 346 may be eliminated. In IFFT330, a carrier is assigned to each input signal and the input signalsare inverse fast-Fourier-transformed. The resulting transformed signalis sent to Analog Front End 350 that interfaces with the power line 116through the power plug 354.

The lower blocks of FIG. 3 are used for data reception. AFE 350 receivesa stream from one or more clients over the power line 116. This receiveddata are fast-Fourier -transformed by FFT 360, demodulated byDemodulator 364 and converted to serial data by Parallel-to-Serialconverter (P/S) 368. The result is de-interleaved by De-interleaver 372,error-corrected by Forward Error Correction (FEC) Decoder 376 and sentto Bus Interface 304.

In a similar manner, received data from FFT 360 for a second data streamare fast-Fourier -transformed by FFT 360, demodulated by Demodulator 380and converted to serial data by Parallel-to-Serial converter (P/S) 384.The result is de-interleaved by De-interleaver 388, error-corrected byForward Error Correction (FEC) decoder 392 and sent to Bus Interface304. As with the transmission side, if components 364 through 376 arefast enough to process two streams, components 380 to 392 are notrequired. PLC Interface 250, thus, simultaneously transmits or receivestwo independent data streams using different carriers, in accordancewith certain embodiments consistent with the present invention.

FIG. 4 shows an exemplary embodiment of Client 108 or Client 112 (e.g.,Client 108 is shown). A Power Line Communication Interface (PLC IF) 402receives a data stream from server 104 and sends the received datastream to Decoder 406 through bus 410. Decoder 406 decodes the streamusing its associated Memory 414. The resulting decoded video signal isconverted to analog using Digital to Analog converter 420 for display ona Display 424. The resulting decoded audio signal is converted to analogin D/A 430, amplified in Amplifier 434 and sent to one or moreLoudspeakers 440. PLC Interface 402 may include an encrypter and adecrypter (not shown) to encrypt transmitted data and decrypt receiveddata. In this embodiment, all of the communication is encrypted beforesending to the power line and decrypted after receipt from the powerline 116.

The user can input commands using keypad 450 or remote commander 454.Keypad 450 sends command to a CPU 460 through interface 464 and bus 410.CPU 460 operates under control of one or more computer programs storedin Memory 466. Similarly, remote commander 454 sends commands to CPU 460through interface 468 and bus 410. CPU 460 controls each componentconnected to or through bus 410. PLC Interface 402 can have the samecomponents illustrated in FIG. 3. If the client does not have tosimultaneously send two streams, components 334 through 346 may beomitted.

In the proposed OFDM-TDMA system, “tone maps” are used to identifycarriers that are used for communication between a transmitter and areceiver. The transmitter and receiver frequently exchange a tone map,for example, on a periodic basis of every 5 seconds, so that thetransmitter and receiver each know what carrier frequencies to use tocarry out communications. The tone map table can be renewed every timetone maps are exchanged. The transmitter sends transmission data with atone map to the receiver. From the tone map, the receiver knows thecarriers and Fourier-transforms used for the transmitted data.

FIG. 5 depicts an exemplary tone map shown in table form wherein timeslots are shown as columns on the table. The rows indicate carriers. Forsimplification, this illustrative embodiment depicts only eight carriers(carriers #0 through #7) and seven time slots (time slots S0 through S6)in FIG. 5, but it will be apparent to those skilled in the art uponconsideration of the present teaching that actual systems may use anynumber of such carriers, and it is contemplated that much larger numbersof carriers (e.g., more than 100 carriers) will generally be used. TheIFFT 330 described above stores data representing this table. Based onthe table, IFFT 330 assigns carriers to input signals.

Due to the nature of the power line communications medium, there arefrequently carriers that exhibit high levels of interference orattenuation such that these carriers are unusable for data communicationbetween certain transmitters and receivers. However, these carriers maybe usable between the same transmitter and different receivers. Thus,when a transmitter communicates with a receiver, the transmittertransmits only over “available carriers”—that is, carriers that are ableto support data communication with some degree of reliability betweenthe transmitter and receiver. The other “unavailable carriers” in thesame time slot are left unused in the proposed OFDM-TDMA system. Inaccordance with certain embodiments consistent with the presentinvention, these unavailable carriers can in fact be used and areassigned to another stream sent to another receiver.

FIG. 5 illustrates a tone map table in which the transmitter of interestsends data to two different receivers using time slots S0 and S1respectively in a manner contemplated by a conventional interpretationof TDMA. In this example, the transmitter uses five carriers to send adata stream to the receiver. The five dotted blocks in time slot columnS0 indicate the available carriers, #1, #2, #4, #5 and #6 are used fortransmitting this data stream to the receiver using time slot S0). Thetransmitter also uses five carriers to communicate with a secondreceiver. The five hatched blocks (#0, #2, #3, #4 and #6) in time slotS1 depict the carriers used for communication with the second receiver.When the network is not busy and there are adequate available slots, thetransmitter may use a slot for each stream. However, when the network isbusy, the transmitter manages time slot assignment so that time-criticaldata such as isochronous data streams are given high priority.

In accordance with an embodiment consistent with the present invention,unused carriers are assigned to non-time-critical, asynchronous datastreams and a time slot is saved for a time-critical data stream. Thisis illustrated in FIG. 6. If the stream in time slot S1 is nottime-critical, carrier #0 and #3 in time slot S0 can be used to carrydata destined for another receiver than that normally assigned to slotS0. Thus, time slot S0 carries two streams destined for two receivers. Adata frame is associated with S0 and has two destinations, the firstreceiver and the second receiver. Also the data frame contains carrierinformation that specifies which destination receiver uses which of thecarriers. As a result of this, carriers #0 and #3 can be used to sendinformation destined for the second receiver during the time slot S0.Therefore, two carriers are used for the second stream destined for thesecond receiver during time slot S0. This frees up two slots from timeslot S1 to thereby increase the bandwidth thereof and increase theactual throughput of data during the time slot S0. The empty time slotsin S1 are then available to be similarly utilized to enhance thethroughput of the system.

When independent data streams from the transmitter share the samedestination, they may share a time slot, in accordance with certainembodiments consistent with the present invention. In one example, thetransmitter may send an audio/video stream and control commands to thesame receiver. Control commands are sent as an asynchronous stream,whereas the audio/video stream may be isochronous. When the network isnot congested, the transmitter may send the two streams using twodifferent time slots. However, when the network is congested, the twoslots can be merged into one slot. This is depicted in the example ofFIG. 7 and FIG. 8.

The five dotted blocks (carriers #1, #2, #4, #5 and #6) in time slot S0indicate available carriers for communication between the transmitterand the receiver. In accordance with certain embodiments consistent withthe present invention, one of the carriers, e.g., carrier #6, isassigned to the asynchronous stream during time slot S0. The blockhaving the vertical hatching marks indicates this time slot and carriercombination. Carriers #1, #2, #4 and #5 are used for the first stream.Usually, control command communication (i.e., a control stream) is shortand not time-critical, therefore it is wasteful of bandwidth to assign awhole time slot for such a short command. Although the bandwidth for thefirst, isochronous stream in time slot S0 may be narrower, the time slotassigned for the second stream is now available for the first stream. Asa result, carriers and time slots can be used more efficiently, inaccordance with certain embodiments.

It may be desirable to limit the bandwidth available for carrying thesecond stream by limiting the bandwidth to no more than, for example,10% of all available carriers, but other limits may be suitabledepending upon the exact implementation. The data frame of S0 has onlyone destination. As discussed previously, the data frame associated withtime slot S0 can be used to carry information that determines whichstream uses which carrier(s) during the time slot.

In view of the above discussion of the assignment of carriers, a timeslot assignment algorithm consistent with certain embodiments of thepresent invention is depicted in FIG. 9, which is made up of FIG. 9A andFIG. 9B. The previous discussion generally described how carriers areassigned. This flow chart 500 describes an algorithm that assigns a timeslot for each stream. The algorithm is applied at 504 to each streamevery time tone maps are exchanged, for example, every 5 seconds. Also,the algorithm can preferably be performed when a new stream starts or anexisting stream terminates. If the stream is a new stream at 508, theprocess goes to 512. If an empty slot is available at 512, the slot isassigned for the stream at 516 and the process ends at 520. If no emptyslot is available at 512, the process proceeds to 524. If the stream isasynchronous at 524, the process goes to 528. If the stream issynchronous, the process goes to 532. At 528, if there is a slot thathas the same destination (receiver), the slot is assigned to the newstream at 516. At 516, some of available carriers in the time slot areassigned for the new stream. If “no” at 528, the process seeks anotheravailable slot at 536. If another slot is found, it is assigned to thenew stream at 516. If no available slot exists at 536, the transmittermay provide a busy message, for example that is displayed on the display218 at 540 and the transmission is refused.

At 508, if the stream is not a new one, its tone map is checked at 544.If there is no change in the tone map, no action is needed and theprocess ends at 520. If there are change(s) in the tone map at 544, theprocess checks to see whether the new carriers in the tone map areavailable at 548. (Note that some carriers might be already used byanother stream.) If available, all carriers are assigned at 516 and theprocess ends at 520. If new carriers are not available at 548, all thecarriers assigned for this stream are released at 552 and the stream isprocessed as a new stream starting at 512 as described above.

If the stream is isochronous at 524, control passes to 532 (of FIG. 9B).An asynchronous stream, which has lower priority than an isochronousstream will be stopped and instead the isochronous stream will get thetime slot(s). Time slots assigned only for an asynchronous stream arechecked at 532. If such a slot is found, the transmitter stops theasynchronous stream at 560. Then, the slot is re-assigned for thesynchronous stream at 516. At 568, another slot is re-assigned for theasynchronous stream by calling the current algorithm recursively. At532, if no slot is available, the transmitter may indicate a busymessage on the display 218 and refuses the isochronous transmission at540 and the process ends at 520.

A transmitter may often broadcast the same stream to multiple receivers.For example, the transmitter may send background music data and eachreceiver receives and decodes it. Because signal conditions for eachnetwork path is not the same, available carriers are not necessarilycommon in the receivers. In the proposed OFDM-TDMA scheme, thetransmitter sends the same data repeatedly to each receiver based on thetone map. That is, the same message may occupy multiple carriersspanning multiple time slots to transmit the same message repeatedly.This redundancy is not negligible when there are many receivers,especially, when the network is busy. Such situation can result in aserious network congestion. In accordance with certain embodimentsconsistent with the present invention, commonly available carriers areused to create a broadcast mechanism. When there are few or no commonlyavailable carriers, two time slots can be merged into one to cut thenumber of time slots in half.

FIG. 10 shows an example tone map table for broadcast by the proposedOFDM-TDMA system. In this example, the transmitter sends a stream tofour receivers. Time slot S0 is for the first receiver and carriers #1,#2, #4, #5 and #6 are available. Data D0 through D4 are assigned to eachcarrier. The next time slot S1 is for the second receiver. Carrier #0,#1, #2, #3, #4 and #6 are used to send Data D0 through D5. Similarly, S2and S3 are used for the third and the fourth receiver, respectively. Inaccordance with this scheme, each data block is sent four times—once toeach receiver creating a situation in which bandwidth is wasted byredundant transmissions.

FIG. 11 shows an example of a broadcast tone map table used by certainembodiments consistent with the present invention. In this embodiment,the system detects that there are commonly available carriers for allfour of the target receivers (See FIG. 10). The carriers #1, #2, #4 and#6 are commonly available carriers for all four receivers and aredepicted as surrounded by bold lines. In accordance with thisembodiment, these four carries and two slots are used to send data D0 toD7. The multiple recipients are called out in the frame structure usedto send slots S0 and S1. This arrangement saves two time slots over thearrangement shown in FIG. 10. Moreover, the system of FIG. 10 is at bestable to send D0 to D5 (i.e. six segments of data) using four time slots,while the system depicted by FIG. 10 can send D0 to D7 (eight segmentsof data) to all four receivers using only two time slots.

When few carriers are commonly available, this approach does not providethe above benefits. This is especially the case, if the number of commoncarriers is less than a half of the maximum available number ofcarriers. For example, if the maximum number of carriers is six in S1and S3 and the number of common available carriers is less than 3, 3 ormore slots are used and no benefit is obtained. In this case, two slotscan be merged into one. FIG. 12 shows an example of a worst-casescenario. In this example, the four receivers are shown to share nocommon carriers. Carriers #2 and #5 (enclosed by bold lines) arecommonly available between slots S0 and S1. FIG. 13 shows a mergedresult. Carriers #2 and #5 carry Data D0 and D1 to both receivers (thereceivers associated with slots S0 and S1). Carrier #0 is assigned tosend D2 to the second receiver. The first receiver cannot receivecarrier #0. Carrier #1 sends D2 to the first receiver. Carrier #3 and #4sends D3 to each receiver, respectively. Similarly, carrier #5 and #6sends D4. The data frame of S0 is configured to have two destinations.The data frame also contains carrier information that the receiver usesto determine which carriers contain data destined for it. In the sameway, S2 and S3 in FIG. 12 are merged into S2 shown in FIG. 13. S1 and S3in FIG. 13 can be used for other communications or S1 can be usedinstead of S2.

FIG. 14 shows a time slot assignment algorithm 600 for broadcastcommunications starting at 604. The number of common carriers is checkedat 608 and if the number is equal to or larger than a half of themaximum number of carriers (or equal to or larger than some otherthreshold number of carriers), control passes to 612. At 612, a new slotnumber is calculated such that the maximum number of carriers is dividedby the number of common carriers. The result is rounded up to theclosest integer. For example, in case of FIG. 10, the result of divisionis 6/4=1.5, which is rounded up to 2. At 616, actual time slots areassigned. The stream of data is divided among the available commoncarriers at and assigned accordingly at 620 in the same manner as wasdescribed previously. The process ends at 624.

AT 608, if the result is less than a half of the maximum number ofcarriers (or other threshold number of carriers), control passes to 630.A number of slots is determined by calculating half (or other fraction)of the original number of slots, and this number of slots is assigned.If the value is not an integer, it will be rounded up to the closestinteger. In the example of FIG. 12, the result of the division is 4/2=2;Thus, the number of slots is two. Pairs of the time slots are mergedinto a single slot at 634. The stream of data is divided to each of thecarriers at 638 and the process again ends at 624.

This algorithm can be applied to each stream every time tone maps areexchanged, for example, every five seconds. Also, the algorithm can beperformed when a new stream starts or an existing stream terminates.

Those skilled in the art will appreciate that many variations ofembodiments of the present invention are possible without departing fromthe invention. For example, in one variation, three or more streams canshare a single time slot. Embodiments of this invention can also beapplied not only to power line networks, but also to wireless, phoneline, cable or any other networks. Embodiments consistent with thisinvention can also be applied to FDMA (Frequency Division MultiplexAccess). In an FDMA system, carriers and time slots change places. Timeslots on the same carrier are assigned to two or more streams.

Thus, in accordance with certain embodiments consistent with the presentinvention, when the network is busy, two or more independent streams areassigned to one time slot based on time criticalness of each stream.Time slots and carriers can be efficiently and dynamically allocated.Also, using common carriers, in certain embodiments consistent with theinvention, can reduce redundancy of multiple broadcast transmissions. Inthe case of few common carriers, two or more time slots can be mergedinto one to reduce the number of 30 total time slots needed. With smalladditions of hardware and software, transmission efficiency will beimproved in certain embodiments.

Those skilled in the art will recognize that the present invention hasbeen described in terms of exemplary embodiments that are based upon useof a programmed processor such as CPU 264 and CPU 460 with program codestored in HDD 234 or memory 274 and memory 466. However, the inventionshould not be so limited, since the present invention could beimplemented using hardware component equivalents such as special purposehardware and/or dedicated processors, which are equivalents to theinvention as described and claimed. Similarly, general purposecomputers, microprocessor based computers, micro-controllers, opticalcomputers, analog computers, dedicated processors and/or dedicated hardwired logic may be used to construct alternative equivalent embodimentsof the present invention.

Those skilled in the art will also appreciate that the program steps andassociated data used to implement the embodiments described above can beimplemented using disc storage as well as other forms of storage such asfor example Read Only Memory (ROM) devices, Random Access Memory (RAM)devices; optical storage elements, magnetic storage elements,magneto-optical storage elements, flash memory, core memory and/or otherequivalent storage technologies Without departing from the presentinvention. Such alternative storage devices should be consideredequivalents.

The present invention, as described in embodiments herein, isimplemented using a programmed processor executing programminginstructions that are broadly described above in flow chart form thatcan be stored on any suitable electronic storage medium or transmittedover any suitable electronic communication medium. However, thoseskilled in the art will appreciate that the processes described abovecan be implemented in any number of variations and in many suitableprogramming languages without departing from the present invention. Forexample, the order of certain operations carried out can often bevaried, additional operations can be added or operations can be deletedwithout departing from the invention. Error trapping can be added and/orenhanced and variations can be made in user interface and informationpresentation without departing from the present invention. Suchvariations are contemplated and considered equivalent.

While the invention has been described in conjunction with specificembodiments, it is evident that many alternatives, modifications,permutations and variations will become apparent to those skilled in theart in light of the foregoing description. Accordingly, it is intendedthat the present invention embrace all such alternatives, modificationsand variations as fall within the scope of the appended claims.

1. A time slot and carrier allocation method for time division multipleaccess (TDMA) multiple carrier communications, comprising: determiningfrom a tone map that first and second time slots are generally allocatedto a first and a second receiver respectively; determining from the tonemap that the first and second receivers are able to receive using acommon set of carriers; determining that a single data stream is to betransmitted to the first and second receivers; transmitting a new tonemap to the first and second receivers that specifies that the first andsecond receivers are to receive the single data stream using the commonset of carriers during one or more designated time slots; wherein thenumber of common carriers is greater than a threshold number ofavailable carriers, and wherein the threshold number comprisesapproximately 50% of available carriers; and wherein a number of unusedcarriers allocated to the control stream of data is less than aspecified maximum, and the specified maximum comprises approximately 10%of available carriers.
 2. The time slot and carrier allocation methodaccording to claim 1, further comprising transmitting a control streamof data to the first and second receivers using the common carrier. 3.The time slot and carrier allocation method according to claim 1,wherein the single stream of data comprises audio/video data.
 4. Thetime slot and carrier allocation method according to claim 1, whereinthe communication comprises an Orthogonal Frequency Division MultiplexedTDMA communication.
 5. The time slot and carrier allocation methodaccording to claim 1, wherein the new tone map specifies that an unusedcarrier is to be reallocated to a plurality of other streams of data. 6.The time slot and carrier allocation method according to claim 1,further comprising transmitting the single data steam using the commonset of carriers during the designated time slots.
 7. The time slot andcarrier allocation method according to claim 1, wherein the tone mapdesignates that the first and second receivers receive the single datastream using merged time slots.
 8. An electronic storage medium storinginstructions which, when executed on a programmed processor, carry out atime slot and carrier allocation method according to claim
 1. 9. Themethod according to claim 1, wherein the communication is carried out ina power line communication system.
 10. A time slot and carrierallocation method for time division multiple access (TDMA) multiplecarrier communications, comprising: determining from a tone map thatfirst and second time slots are generally allocated to a first and asecond receiver respectively; determining from the tone map that thefirst and second receivers are able to receive using a common set ofcarriers; determining that a single data stream is to be transmitted tothe first and second receivers; transmitting a new tone map to the firstand second receivers that specifies that the first and second receiversare to receive the single data stream using the common set of carriersduring one or more designated time slots, wherein the new tone mapspecifics that an unused carrier is to be reallocated to a plurality ofother streams of data; transmitting the single data stream using thecommon set of carriers during the designated time slots; transmitting acontrol stream of data to the first and second receivers using thecommon carrier; and wherein the number of common carriers is greaterthan a threshold number of available carriers, and wherein the thresholdnumber comprises approximately 50% of available carriers, and whereinthe tone map designates that the first and second receivers receive thesingle data stream using merged time slots, and wherein the singlestream of data comprises audio/video data; and wherein a number ofunused carriers allocated to the control stream of data is less than aspecified maximum, and wherein the specified maximum comprisesapproximately 10% of available carriers, and wherein the communicationcomprises an Orthogonal Frequency Division Multiplexed TDMA power linecommunication.
 11. The method according to claim 10, wherein thecommunication is carried out in a power line communication system. 12.An electronic storage medium storing instructions which, when executedon a programmed processor, carry out a time slot and carrier allocationmethod according to claim 10.